While he lay on the turf, unable to roll from danger, a following horse stamped on his head.

So traumatic was the injury, as he remained apparently unresponsive in a coma, the doctors advised that his life support should be switched off, a move that prompted the Racing Post to publish his obituary.

The device, however, was left on while his parents travelled from Ireland. But because his father refused to come by plane, instead of six hours to get to Warrington, the Murphys took 24. And after 22 hours their son showed the first twitch of life. Subsequently his mind may well have erased the thought that he only survived because his dad was afraid of flying.

But the odd thing is, it was not just the accident that was expunged from his memory. Long after he had recovered, long after he learned to walk, to run, to ride again, long after he forged a new career as a hugely successful property developer living in Barcelona, the time he was at the peak of the riding trade remains a complete blank.

“Four years, six months, four days: gone,” he says. “I can remember up to the point I became successful. But it wiped out all the best parts of my career. It meant for years I pretended what had happened to me never happened. Because I couldn’t remember. When people talked about it I’d acknowledge it, but never engage. I removed myself from it.”

Yet now, two decades after the accident, he has just published his autobiography. It seems an unlikely proposition: the memoir of a man who can’t remember. “Maybe that’s why it’s taken so long,” he says, in his publisher’s office. “There are so many pages of my story torn out. I never wanted to do a book. I turned the idea down many times. I’d walked away, become someone different. I didn’t want to go back there. How can you assess the psychology of someone who doesn’t talk about what’s happened to them?”

The beautifully tailored suit he is wearing suggests he didn’t need the money. But in the end he was persuaded by his ghost writer, an American academic called Ami Rao. She became his ghost in every sense, trying to inhabit his past in the quest to help him recover the lost times.

The result is Centaur, a brilliant, bold and at times brutal examination of the process of re-constructing his memory. “What appeared to happen to me was I had an accident and I recovered. It wasn’t as simple as that,” he suggests. “It was a deeply personal battle. I didn’t have a fight going on within me I had a war. I chose to fight this war on my own.”

In the long process of recovery, he cut himself off completely from his past. Although strong enough physically, he only rode one comeback race. He won it and then walked away from racing. Ami Rao, however, made him confront who he was, made him look at every single piece of written or visual evidence of his riding prowess.

Murphy pictured a year after his accidentCredit: GETTY IMAGES

“I’ve never cried so much as I have doing this,” he admits. “We talked to so many people about me. Their memories of what happened, it was like I’m a third party listening to this story. Really? That was me?”

One of the things he read during the process was his own obituary. “They were very kind about me,” he says of the Racing Post eulogy. “No complaints there.” As he recovered, Murphy had deliberately removed himself from those who had been central to his life before the accident. In the reconstruction of his memory, Ami Rao contacted all of them, several of whom had not heard from him in nearly 25 years.

“That was the amazing thing about this book,” he says. “Everybody we spoke to was desperate to talk. It was like they had finally been given permission.”

He discovered all sorts of things in the process. Like the fact his accident had happened the day after his hero Ayrton Senna had been killed and that he had apparently been filled with foreboding as he got ready to ride. Or like the way his fellow riders had reacted. “It seems when the doctor brought my helmet in and it seeped blood on to the table, every jockey in the weighing room that day, their blood went cold. You can’t imagine that type of scene. I certainly hadn’t.”

Ami Rao also contacted Joanna, Murphy’s then-girlfriend, who frantically tried to call him 20 or 30 times the afternoon of the accident, only for her calls to be ignored by the other jockeys, too traumatised to answer the phone ringing in his kitbag. She stood by him throughout his recovery, but they broke up soon after. The problem was Murphy had no memory of her before his accident. Nothing at all. Which was something his seven-year-old daughter struggled to understand.

Declan Murphy's book is "a brilliant, bold and at times brutal examination of the process of re-constructing his memory"Credit: SUNDAY TELEGRAPH

“My daughter opened the book and found a picture of me with Joanna,” he says. “She said to my wife, ‘Mummy, daddy had a girlfriend’. Then she said to me, ‘Why didn’t you marry her?’ My wife said: ‘Daddy had an accident and he can’t remember Joanna’. And you know what my daughter said? ‘But her picture’s in his book’.”

As he moved on in life, leaving his past behind, Murphy says the fact he was such a successful jockey became ever less significant. “I’m absolutely a different person. I have never used racing as a currency to trade in. Never. And I had a great career.” That said, he does admit that some of the mental requirements needed to become a top rider have been useful in his subsequent life.

“I absolutely used the disciplines I used as a jockey. But I think I had those anyway, and would have applied them to whatever I have done. I certainly had to be very disciplined in my recuperation.” Mentally, he says, his recovery was easily the most difficult thing he has ever done. Or at least that he can remember doing.

“I had to make sacrifices that you can’t imagine ever having to make. Yes, of course, there were consequential effects to that. Everybody said I changed. I became very private. I became obsessed with trying to create an identity for myself. That’s the thing when you don’t have a memory: you don’t have anything that tells you that you are the person you are.”

Now at least the memories are there in his book. Even if not in his mind.

Centaur by Declan Murphy and Ami Rao is published by Doubleday (£16.99)